Almost all automotive air conditioning clutches are powered by a belt driven pulley, a pulley that freely rotates about the drive shaft of the compressor until an annular iron armature is pulled, by an electromagnetic coil, against a friction disk of the pulley with enough force to cause the two to stick frictionally together. The armature, in turn, is physically supported on a central hub of the compressor drive shaft by an armature support mechanism that holds the armature coaxially to and spaced away from the pulley friction disk, close enough to be pulled into and against it when the clutch is actuated. The armature support mechanism must be radially and circumferentially rigid enough to successfully transfer drive torque from the co rotating pulley and armature to the shaft. It also must be axially flexible and resilient enough to allow the armature to be pulled toward and then rebound from the pulley as the clutch rams on and off. Ideally, the armature would be supported on the shaft hub by a mechanism that not only transferred torque and provided axial flexibility, but which also provided a measure of torsional flexibility and resilience, enough to at least cushion the initial shock of armature engagement with the pulley. The torsional flexibility in known torque cushions often is reflected in a radial flexibility that jeopardizes the radial alignment of the armature, however. The initial armature engagement not only creates a rapid spike in torque that needs cushioning, it is also accompanied by a degree of initial rubbing and slippage between the outer face of the pulley friction disk and the inner face of the armature, before the two completely stick together. This creates a good deal of heat and, with heat, extra rubbing wear. No special provision is made, in known armature support mechanisms, to cool the armature, and many actually retard its cooling.
The typical armature support mechanism consists simply of a rigid drive plate welded to the compressor drive shaft hub, and three or more simple leaf springs riveted at one end to the drive plate, and at the other end to the armature. The leaf springs lie in a plane parallel to the drive plate, and are fairly rigid in that plane, capable of transferring torque between the armature and drive plate, and ultimately to the compressor drive shaft. But the springs can flex easily in the axial direction, in cantilever fashion, since they are thin in the axial direction. Examples may be seen in several issued patents, for example, U.S. Pat. No. 5,046,594 to Kakinuma, where armature 26 is joined to a hub mounted drive plate 28 by three thin leaf springs 27. This is a very common design. The drive plate 28, in such a design, is typically round, or triangular, as in U.S. Pat. No. 4,337,855, and is usually uninterrupted by any large holes or voids, except where the ends of the leaf springs are riveted to it. Although the drive plates may be small enough to leave some of the area of outer face of the armature exposed to ambient air, and therefore able to cool passively by radiation, the leaf springs are so thin that their edges would not disturb enough air as they spun to act as fan blades would to actively cool the outer face of the armature. Nor would the drive plate itself provide any fanning action per se, both because of its size and shape. There is no recognition in such designs that the drive plate or leaf springs could or should do any more than flexibly support the armature and transfer torque.
A similar design may be seen in U.S. Pat. No. 4,296,851, with a typically round drive plate 53, but with C shaped leaf springs, rather than straight. Some designs, such as that shown in U.S. Pat. No. 2,982, 385, use a spring disk 54 riveted to a drive plate 52, rather than individual springs, while others, such as that shown in U.S. Pat. No 3,055,475, use a single disk with individual spring members stamped integrally out of it. These designs still provide no fanning action to cool the armature and, in some cases, actually cover most or all of the outer face of the armature so as to retard it's cooling. One design, shown in U.S. Pat. No. 5,119,915, has a leaf spring mount that consists of three short, radial arms 42 that are formed integrally with the central hub, rather than a flat drive plated welded to the hub. Thin leaf springs are attached to the arms 42. While the arms 42 would create some paddling of air, they do not extend out radially far enough over the armature that they would fan any significant air over it to cool it. Again, this is not surprising, since there is no recognition that the armature support and spring mechanism could or should do anything to cool the face of the armature.
A significantly different approach to supporting the armature is to combine the drive plate and springs into a single axially flexible disk or plate, which completely, or almost completely, covers the outer face of the armature. This has the advantage of eliminating parts, and, in the case where the plate itself is made of a torsionally resilient material, provides a torque cushion. It essentially eliminates any potential for cooling the face of the armature, however, and in fact would insulate and retard it from cooling. Again, this is not surprising, since there is no apparent recognition that the armature support could also cool the armature that it supports. An example of such a design may be seen in U.S. Pat. No. 5,370,209, where a hard plastic disk covers the entire face of the armature. Another design, shown in U.S. Pat. No. 5,390,774, covers almost the entire face of the armature with a thick rubber cushion.